Abstract
A new method to synthesize noble metal nanoparticles has been developed whereby an alcohol-type surfactant, sodium alkyl sulfate (SCnS, n=8,10,12,14), is used as the reductant, and there is no need for an external reducing agent. In this method, metal ions including Pd, Pt, Ru and Ag are reduced to zero-valence atoms by self-generated long carbon-chain alcohol inside the micellar core and then hydrophilic metal nanoparticles form. By this method, in the Pd case, by changing the carbon chain length of the surfactant, the diameter of the nanoparticles can be controlled. The longer the carbon chain length is, the shorter is the particle diameter. Additionally, a highly ordered 3D “spheres-around-sphere” type nanostructure is found in the Pd nanoparticles/SC10S system. This configuration involved the transformation of the liquid crystal phase of the micelle molecules from micellar to lamellar. In the Pt case, the particle diameter can be controlled between 1 and 3 nm. In the Ru case, the time to form particles is found to be shorter than that to form Pd, Pt or Ag particles and particles diameters are always around 2 nm regardless of the surfactant used. Finally, in the Ag case, by UV-Vis spectrum, the surface plasmon resonance band at about 400 nm accompanying with particle nucleation and growth is found to be continuously intense and shift toward red. Another important finding is that the nanoparticles which are hydrophilic, hydrophobic or both can be effectively prepared by regulating the reflux time in this method. The transformation in surface property from hydrophilic to hydrophobic results from the formation of ester, which adsorb on the particle’s surface and improves dispersibility in the organic medium. The feasibility of using this newly synthesized Pd nanoparticles as activator for electroless copper deposition has also been examined. In this study, copper is successfully deposited on a wafer with 0.25 um microtrench after activation with the Pd/Sds solution. In addition, the effects of surrounding functional group and the particle size on the kinetics of electroless copper deposition were studied by electrochemical quartz crystal microgravimetry (EQCM). The performance of Pd nanoparticles was also compared with the traditional Pd/Sn colloid-type activator. Besides, when hydrophilic Pt nanoparticles prepared by this synthesis method are tried to be activators for electroless copper deposition, the particles are found to exhibit excellent activity.